Aikido is the transformation of violence into peace. The opponent has a hostile intention, and wants to use violent ways (smashing your head, for ex.) to achieve his goal. The accomplished aikidoka does not oppose his own strength to his adversary's. He attracts him to guide him "softly" to a situation where violence will not be of any use (pinned by ikkyo, for ex.) and where he will have to give up his initial intention and to relax.

IMHO, Aikido is not a tool, because a tool does not transform its user : it just serves his purpose regardless of his ethical value. On the contrary Aikido is a philosophy of mind and body, and brings the practitioner to reconsider his ways and reasons of acting (ethics) towards non-violence.